考虑淤堵效应的塑料排水板单元体真空固结理论及其应用技术

Vacuum consolidation is an effective method for improving soft clayey deposit. While for dredged clayey soils not finishing the self-weight induced consolidation, vacuum consolidation often cannot achieve the designed result. There are two main reasons for this. One is that the existing consolidation theory cannot consider the consolidation induced clogging effect. Another one is that the consolidation behavior of the clayey soils with high initial water content is significantly influenced by its water content and chemicals in the pore water, but there is no theoretical method to quantitatively evaluate the effect. To increase the design accuracy and enhance the effect of vacuum consolidation for clayey soils with high initial water content, a new consolidation theory which can consider the effect of the clogging and its application technics are urgently needed. To establish this system, following key scientific issues have to be resolved through experimental study, theoretical and numerical analyses. 1. Mechanism of clogging and a consolidation theory can consider the clogging; 2.A method for quantitatively evaluating the effect of initial water content and chemicals in the pore water on the properties of consolidation and compression of the clayey soils; 3.An optimum procedure of applying vacuum pressure to result in less clogging and maximize consolidation effect and a method for selecting effective and environment friendly additive.

真空固结是处理软黏土地基的一个有效方法。但对高含水率黏性土，真空固结往往达不到设计的固结效果。其主要原因有两个。一个是现有塑料排水板(PVD)单元体固结理论无法考虑由真空压力引起粒径分级而形成的物理淤堵，和由不均匀固结引起的固结“淤堵”的影响。另一个是高含水率黏性土的固结及压缩特性受其初期含水率及孔隙水化学成分的影响很大，但目前还没有一个对此类影响进行定量评价的方法。为提高对高含水率黏性土的真空固结效果及设计精度，需要建立一个能考虑淤堵效应的固结理论及能考虑初期含水率及孔隙水化学成分影响的应用技术。为此，需解决以下几个关键科学问题：（1）探明物理淤堵和固结“淤堵”发生的机理并得出考虑其影响的PVD单元体固结理论;（2）高含水率黏性土的初期含水率及孔隙水化学成分对其固结及压缩特性影响程度的定量评价方法（3）以最小淤堵效应，最大固结效果为目标，建立真空压力优化加载方式及选择有效絮凝添加剂的方法

本项目通过模型固结试验，土体微结构观察，有限元解析及理论分析对用真空及荷载预压法改良黏土及淤泥地基过程中塑料排水板（PVD）周围发生淤堵现象的机理，缓解淤堵现象的影响的方法，开发能考虑淤堵效应的固结理论及计算交通（循环）载荷引起的PVD单元体固结变形的方法方面进行了系统研究，得出了3个主要成果。（1）淤堵发生的机理有两个。其一为不均匀固结引起的PVD周围低透水性土层；其二为局部变形引起的PVD周围土体的分散型微结构的形成，即片状黏土粒子沿PVD表面配列进一步减小水平向透水系数。根据这些机理开发了能穿过PVD周围低透水性土层的带翼塑料排水板（WPVD）。还建立了在土体中添加带阳离子的化学添加剂，以促进絮凝状土体微结构的形成从而减少淤堵效应的方法。（2）建立了一个能考虑PVD周围淤堵效应的非线性大应变固结度计算方法。此方法可用Excel表格实现所有计算，所以方便实用。（3）建立了交通（循环）载荷下PVD单元体固结沉降的计算方法。此法用一个等价静荷载来代替交通载荷的作用，所以非常简便实用。是目前唯一能用Excel表格计算交通荷载引起的固结沉降的方法。这些成果可用于提高用预压法改良黏土及淤泥地基的设计精度及效率，以及为选择黏土地区道路等基础设施的维护方法提供基础数据，从而服务于交通运输基础设施的建设及维护。